In general, William Donohue of the Catholic League for Religious and Civil Rights is one of those figures to whom we've become accustomed in American life, an identity politics ambulance chaser. He's like Al Sharpton or Abe Foxman or any number of other figures. When their group is somehow defamed or derided by a sitcom or novel or politician's Freudian slip, they mount their steeds, instantly issuing the fearless press release and rushing onto the national airwaves to inveigh against the calumny at hand.

That's one thing. Whatever one thinks of it, it serves what we might call a function in a multicultural and open society. One can pay attention or turn the channel.

But what Donohue said the other night is quite another. It was probably the most disgusting thing I've ever heard an American public figure say.

The venue was the Larry King chat show on CNN. The topic was the Catholic church abuses, and the quadrumvirate of guests included Donohue and his old nemesis Sinead O'Connor, who felt the brush of Donohue's wrath when she tore up that picture of Pope John Paul II back in 1992 (and who did time in one of the infamous Magdalene laundries as a teenager).

Roberts: Bill is good but you cannot link homosexuality to a paedophilia crisis in the Catholic church.Bill Donohue: It's not a paedophilia … most of the victims were post-pubescent …Roberts: You know …Donohue: You've got to get your facts straight. I'm sorry. If I'm the only one that's going to deal with facts tonight so be it. The vast majority of the victims are post-pubescent. That's not paedophilia, buddy. That's homosexuality.Roberts: Bill, I don't think as a person of faith that you really know what you're talking about when it comes to a victim and a survivor. (crosstalk)Donohue: It's not of my opinion. Take a look at the social science data. I never said that most homosexuals are that way.Roberts: No you just said that cut down homosexuals… (crosstalk).Donohue: Yes! Practising homosexuals.

Let's try to break that down (and we haven't gotten to the really shocking statement yet). In a technical and clinical sense, a case can be made for the way Donohue defines paedophilia, which (technically and clinically) is meant to refer to abuse of pre-pubescent boys. Historically, "paederasty" is more associated with teenage boys. Whatever. The important thing is that when it comes to the law, both are illegal, as Donohue surely knows.

But it's when he says "that's homosexuality" that he begins his stroll into the quicksand. It seems obvious that "consensual" is his implied adjective there. He seems clearly to be saying that once a young male attains puberty, he is making a choice.

The hanging question at this point in our dialogue is the age at which Donohue considers puberty to have been reached. If somehow he believes it's 15, then he might make it through this. Fifteen is objectively absurd on its face, of course. But if that was what he thought – well, the age of consent in many states is 16, so it becomes a close call, and for some viewers he has successfully muddied the waters. Throw into the mix here a study by the John Jay College of Criminal Justice in New York, a study to which Donohue referred on the show, saying that most victims were post-pubescent and only a "small percentage" of priests standing accused of molesting pre-pubescent boys.

The question was going to be permitted to hang. But O'Connor butted in, literally raising her hand in an effort to get King's attention:

King: You want to get in? Sinead, go ahead quickly.O'Connor: Can I just ask very quickly if that gentleman, sir I don't know your name … just, I'm not quite sure what post-pubescent means. You mind explaining that to me?Donohue: Explain what?O'Connor: What does post-pubescent mean?Thomas: Post-pubescent…O'Connor: What does post-pubescent…Donohue: Post-pubescent means beyond puberty, OK? In other words you're an adolescent and that's what homosexuals do and most of them the molesters have been homosexuals in the Catholic church (crosstalk).Thomas: So the boys deserved it because they were post-pubescent?Donohue: Now if you want to take that conclusion, I think that's scurrilous. I never said that. Why would you say that about homosexuals?O'Connor: Sorry Larry, at what age does somebody become, you know, post-pubescent in America as a matter of ages?King: What is the age?Thomas: Ah… I don't know. Let's ask Bill. He seems to be the authority on post-pubescency.Donohue: 12, 13 years of age.

First of all it's hard to parse exactly what Donohue means in his response to O'Connor. "You're an adolescent and that's what homosexuals do" is foggy, but I take him to mean that preying on adolescents is what "homosexuals" do. That in itself is an abhorrent sentiment. It's clear that the whole subject gives him the heebie-jeebies and he gets addled even thinking about it.

But it's that "12, 13" that I hope made you gasp. Again, the man is so out of it that it's hard to pin down exactly what he meant. He might have meant that by that age, some boys become volitionally gay, and so having sex with priests is something they choose to do ("that's not paedophilia, buddy. That's homosexuality").

He might have meant that gay priests can't help but be enticed by post-pubescent boys, because that's just how homosexuals are. Whatever he meant, what came out was that he was leaning on a technical clinical distinction about the definition of paedophilia and asserting that the abuse of boys once they've grown pubic hair is in some sense not a problem.

Maybe he was just confused. But that's normally no excuse. Al Campanis was famously confused once on US national television, but it cost him his job, as such confusion has cost others.

Donohue will never lose his. He answers to boards that have been stacked with rightwingers (Dinesh D'Souza, Alan Keyes, Domino's Pizza founder Tom Monaghan). And needless to say this will only get him more television bookings, as hosts attempt to trip him up further, which in turn will only get his spurious league more and more donations. So we'll have to live with him. But that's not as bad as D'Souza, Keyes, Monaghan and the rest having to live with themselves for putting their weight behind a man who has now taken a public position scarcely distinguishable from that of the North American Man/Boy Love Association. The rest of us have to believe that on some level, in some solitary night, these believers have consciences that actually do bother them.

• This article was amended on 5 April 2010. The original referred to Tom Monaghan as "Domino's Pizza chief". This has been corrected.